Backlight adjustment system

ABSTRACT

A preferred embodiment relates to controlling the amount of backlight in an electronic display to account for the temperature in the backlight cavity. Another embodiment relates to a system for controlling the amount of backlight based on both the temperature in the backlight cavity and the amount of ambient light. The embodiments are especially useful in electronic displays which are subjected to cold or warm temperatures and displays which are placed in very bright environments. Exemplary embodiments allow the display to remain visible, while avoiding possible damage due to high levels of heat or cold.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to co-pendingU.S. application Ser. No. 12/124,741 filed on May 21, 2008, hereinincorporated by reference in its entirety.

TECHNICAL FIELD

This invention generally relates to electronic display sensor systemsand in particular to adjustable backlight systems for advancedelectronic displays.

BACKGROUND OF THE ART

Traditionally, advanced electronic display systems have only been usedfor indoor applications, or outdoor applications where the variation intemperature and/or amount of direct sunlight is limited. When thesesystems are moved outside, both elements become significant factors inthe display's ability to accurately recreate an image.

Cold is especially harmful to liquid crystal display (LCD) systems wherethe crystals can actually freeze. Heat is also harmful to manyelectronic displays as the electrical components which drive the displaysystem may overheat and malfunction. Further, direct sunlight can limitthe visibility of the display, as the reflection of the sun off of theviewing surface may be brighter than the light which is generated by thedisplay. Direct sunlight can also heat the display, contributing to theoverheating of electrical components or possible damage to liquidcrystals in LCD applications.

SUMMARY OF THE INVENTION

Exemplary embodiments include a system and method for adjusting thebacklighting on an electronic display based on temperature and luminancemeasurements. Electronic displays typically contain some type of lightsource in order to generate an image on the display screen. This lightsource is often referred to as the display's backlight. Sometimes,fluorescent bulbs may be used or more preferably, light emitting diodes(LED). A backlight system using LED's is disclosed in U.S. Pat. No.7,052,152, herein incorporated by reference.

The amount of light that is required from a display backlight isdependant upon the amount of ambient light that is coming from thesurrounding environment. For example, when the surrounding environmentis very bright, a large amount of light is required from the backlight,as this light must overcome the bright light which is in the environmentand is reflecting off the display surface. In contrast, when thesurrounding environment is very dark, only a small amount of light isrequired from the backlight, as the display's light does not have tocompete with a bright ambient light.

For indoor display applications, the variance is amount of backlight maybe relatively low, as the amount of light inside a room may vary only asmall amount. However, when electronic displays are used outdoors, theamount of ambient light can vary drastically. The ambient light that issurrounding the display can vary anywhere from completely dark at night,to being in direct sunlight during the day. These concerns are amplifiedfor advanced displays which are designed to produce high quality, brightimages with sharp contrast. Thus, in an exemplary embodiment thebacklight of an electronic display is controlled, depending at leastupon the amount of ambient light.

Some sources of backlighting degrade over time. For example, LED's maydegrade over time and emit less light. Exemplary embodiments also allowfor the brightness of a display to adjust based on the degradation ofthe light source.

Also for indoor applications, the temperature that an electronic displayis subjected to will also vary only a small amount. Typically, thesedisplays only see a range of temperatures near room temperature (ex.65-75 degrees Fahrenheit). However, for outdoor applications, displayswill see a very wide range of temperatures. These displays may seetemperatures ranging from well below freezing to well over 100 degreesFahrenheit.

The electronic display backlight is also a significant source of heatfor the display. As mentioned above, too much heat or too little heatcan also damage or destroy an electronic display. Again, this isespecially a problem for large advanced displays, as these devicestypically are required to produce bright, clear images. The amount oflight that is required, typically forces the backlighting assembly toproduce a large amount of light, which typically produces a large amountof heat. Thus, exemplary embodiments also control the level of thedisplay backlighting based on the temperature of the air within thebacklight cavity.

The foregoing and other features and advantages of the present inventionwill be apparent from the following more detailed description of theparticular embodiments, as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of an exemplary embodiment will be obtained froma reading of the following detailed description and the accompanyingdrawings wherein identical reference characters refer to identical partsand in which:

FIG. 1 is a perspective view of an exemplary electronic display.

FIG. 2 is a side plan view of an exemplary embodiment showing componentsof the display system and the control system.

FIG. 3 is a flow chart showing the components for an exemplaryembodiment of the control system.

FIG. 4A is a flow chart showing the logic for controlling the amount ofbacklight based on the amount of ambient light.

FIG. 4B is a flow chart showing the logic for controlling the amount ofbacklight based on the temperature in the backlight cavity.

FIG. 5 is a side plan view of another embodiment where the amount ofbacklighting is not based on the ambient light.

FIG. 6 is a flow chart showing the components for another embodimentwhere the amount of backlighting is not based on the ambient light.

DETAILED DESCRIPTION

Exemplary embodiments include a system and method for adjusting thebacklighting on an electronic display based on temperature and luminancemeasurements.

FIG. 1 shows an exemplary outdoor display which could be subjected tohigh levels of both heat and cold. The viewing surface 100 is containedwithin the display housing 105.

FIG. 2 shows further details about the electronic display and itsassociated components. The display housing 105 may contain all of theassociated components. The viewing surface 100 is again found on thefront of the display housing 105.

Towards the back of the display housing 105 is the electrical devices150 which run the display. These devices may include: motors, circuitboards, resistors, capacitors, wiring, electronic chips, heating/coolingelements, fans, and power sources. In front of the electrical devices150 is the backlight panel 130 and the backlight 120. In this exemplaryembodiment, the backlight 120 comprises LED's, but any form ofillumination will still fall within the scope of the invention. Thebacklight panel 130 provides a mounting surface for the LED's. Thebacklight panel 130 may also contain a highly reflective front surfaceso that the maximum amount of light from the LED's can pass through theviewing surface 100.

Between the backlight 120 and the viewing assembly 140 is the backlightcavity 160. The dimensions of the backlight cavity 160 is typically afunction of the number of backlight LED's 120 and their luminance, sizeof the viewing surface 100, and the properties of the viewing assembly140. The viewing assembly 140 may contain a variety of elements whichare used to generate an image upon the viewing surface 100. In an LCDdisplay for example, the viewing assembly 140 may contain a lightdiffuser, light reflector, several layers of polarizing glass, and aliquid crystal assembly. The precise elements and their arrangement willvary depending on the specific electronic display device being used andits particular application.

In an exemplary embodiment, an ambient light sensor 170 may be locatedoutside of the display housing 105 and in front of, but not blocking thedisplay surface 100. This ambient light sensor 170 measures the amountof light which is contacting the front surface of the display housing105. Although shown at the base of the display in FIG. 2, the ambientlight sensor 170 can be placed anywhere the sensor can measure the lightcontacting the front of the display housing 105, and near the displaysurface 100.

A backlight sensor 171 may be placed within the backlight cavity 160,and measures the amount of light which is luminating from the backlight120. The backlight sensor 171 can be placed anywhere within thebacklight cavity 160, but preferably should be oriented so that it doesnot block any significant amount of light from entering the viewingassembly 140.

Further in this exemplary embodiment, a temperature sensor 175 may belocated within the backlight cavity 160. This temperature sensor 175also can be located anywhere within the backlight cavity 160 or anywhereinside the display housing 105, but preferably should be oriented sothat it does not block any significant amount of light from entering theviewing assembly 140. The wiring 180 for the three sensors is shown atthe base of the display housing 105 and running back to the electronicdevices 150. The wiring 180 can be oriented in a number of ways, with orwithout separate connectors, as is common for one skilled in the art.

FIG. 3 shows an exemplary embodiment with associated components andtheir connectivity. Data from the ambient light sensor 170, backlightsensor 171, and temperature sensor 175 flows into the software driver190. The software driver 190 may be any commercially available controlsystem or microcontroller. Preferably, the software driver 190 comprisesan e²prom (or eeprom), which is commercially available from Digi-Key(www.digi-key.com). The logic for the software driver is discussedbelow, under FIGS. 4A and 4B.

The software driver 190 decides how much power to send to the backlight120. The software driver 190 sends the data regarding the proper amountof power to the power source 195, which generates the proper amount ofpower. A current measurement device 200 may be used to measure theamount of power coming from the power source 195. This information issent back to the software driver 190 and compared to the power datawhich was originally sent to the power source 195 in order to ensurethat the proper amount of power was in fact sent to the backlight 120.If these values do not match, adjustments are made by the softwaredriver 190. Although this embodiment shows a current measurement device,any type of power measurement device will suffice.

Finally, the power is sent to the backlight 120, where the amount oflight generated is again measured by the backlight sensor 171. The datafrom the backlight sensor 171 is again sent to the software driver 190,along with the data from the ambient light sensor 170 and thetemperature sensor 175 as the process is repeated.

FIG. 4A shows an exemplary embodiment for the logic contained in thesoftware driver 190 for adjusting the backlight based on the amount ofambient light. Ideally, a preferred light ratio can be determined whichcompares the amount of light in the ambient surroundings with the amountof light being generated in the backlight cavity 160. For mostapplications, the amount of backlight will need to be greater than theamount of ambient light to ensure that the display can be seen.Preferably, the ratio of ambient light to backlight should be less thanone. (ex. Ratio=ambient light/backlight). However, the precise ratio canvary depending on the particular display, environment, and application.

After a preferred light ratio is selected, it is stored within thesoftware driver 190. The light ratio will also likely have an acceptablerange, such that there is an ideal ratio with a certain amount oftolerance which allows the measured ratio to drift above or below theideal ratio, before any action is taken by the system. The softwaredriver 190 then reads the data from the light sensors and calculates thecurrent light ratio. If the ratio is outside of the accepted tolerancerange, then the system takes action. If the ratio is too low (i.e. thereis too much backlight for the amount of ambient light), the backlight isdecreased. If the ratio is too high, the backlight is increased. If theratio is within the accepted tolerance, the current power to thebacklight is continued.

FIG. 4B shows an exemplary embodiment for the logic contained in thesoftware driver 190 for adjusting the backlight based on the temperaturein the backlight cavity 160. A preferred operating temperature can beselected for the display, which will take into account the type ofdisplay, application, and its environment. This preferred operatingtemperature would again have a tolerance, where there is a minimumacceptable temperature along with a maximum acceptable temperature. Thesoftware driver 190 determines the current temperature from thetemperature sensor 175 and compares this value to the preset min/maxoperating temperature. If the present value is below the minimum, thebacklighting is increased to facilitate the warming of the display. Ifthe present value is above the maximum, the backlighting is decreased tofacilitate the cooling of the display. If the present value is withinthe acceptable range, the present amount of power to the backlightingwill be continued.

Using the amount of backlighting to facilitate the warming or cooling ofan electronic display is very useful in applications where the displayis exposed to a wide range of temperatures, especially high levels ofcold or heat. For example, in an outdoor application where thetemperature of the ambient air becomes very warm (and subsequently warmsthe temperature of the air in the backlight cavity 160) the display maybecome damaged if it continues to run. In typical displays, a thermostatwill simply turn the display off to allow it to cool. However, where adisplay is used as an advertisement tool or for displaying importantinformation, turning off the display will result in a lack ofcommunication of any images whatsoever. Exemplary embodiments allow thedisplay to simply dim itself slightly, to allow the unit to cool whilestill providing some visible image (albeit not as bright, but stillvisible).

This function also aids in protecting a display when the ambient airbecomes very cold (and subsequently cools the air in the backlightcavity 160). Exemplary embodiments allow the display to increase theamount of backlighting, which will typically produce more heat, andsubsequently heat the dangerously cool display.

The embodiments shown in FIGS. 2 and 3 allow the system to control thebacklighting based on both the ambient light and the temperature in thebacklight cavity. FIG. 5 shows another embodiment where the systemcontrols the amount of backlighting based on the temperature in thebacklight cavity, without regard to the amount of ambient light. Thisembodiment lacks the previous light sensors, but contains thetemperature sensor 175.

FIG. 6 shows the various components for this embodiment, again lackingthe light sensors but still containing the temp sensor 175, softwaredriver 190, power source 195, current measurement 200 (optional), andbacklight 120. As the embodiments in FIGS. 2 and 3 conduct the logic inboth FIGS. 4A and 4B, the embodiments in FIGS. 5 and 6 would onlyconduct the logic in FIG. 4B.

It is to be understood that the spirit and scope of the disclosedembodiments are not limited to LCDs. By way of example and not by way oflimitation, embodiments of the present invention may be used inconjunction with displays selected from among LCD (including TFT or STNtype), light emitting diode (LED), organic light emitting diode (OLED),field emitting display (FED), and cathode ray tube (CRT). Furthermore,embodiments of the present invention may be used with displays of othertypes including those not yet discovered. In particular, it iscontemplated that the present invention may be well suited for use withfull color, flat panel advanced LCD displays. While the embodimentsdescribed herein are well suited for outdoor environments, they may alsobe appropriate for indoor applications (e.g., factory environments)where ambient light and thermal stability of the display may be at risk.

Having shown and described a preferred embodiment of the invention,those skilled in the art will realize that many variations andmodifications may be made to affect the described invention and still bewithin the scope of the claimed invention. Additionally, many of theelements indicated above may be altered or replaced by differentelements which will provide the same result and fall within the spiritof the claimed invention. It is the intention, therefore, to limit theinvention only as indicated by the scope of the claims.

What is claimed is:
 1. A system for controlling the backlighting of anelectronic display with a backlight cavity contained within a housing,the system comprising: a backlighting assembly within the backlightcavity of the electronic display; a power source operatively connectedto said backlighting assembly; a temperature sensing device within thehousing; a first light sensing device positioned to measure ambientlight; a second light sensing device within said backlight cavity; and asoftware driver operatively connected to said temperature sensingdevice; said first and second light sensing devices; and said powersource; and wherein the software driver is adapted to decrease the powersource when the temperature sensing device indicates a temperaturehigher than a threshold temperature, measure a light ratio, wherein saidlight ratio is defined as the ratio of the amount of light contactingthe front surface of the housing to the amount of light within thebacklight cavity; increase the power source when the light ratio exceedsa maximum preferred light ratio; and decrease the power source when thelight ratio falls below a minimum preferred light ratio.
 2. The systemof claim 1 further comprising a power measurement device operativelyconnected between said power source and said backlighting assembly andproviding power data to said software driver.
 3. The system of claim 1wherein said software driver comprises an eeprom.
 4. The system of claim1, wherein the backlight assembly comprises: a mounting element; areflective element covering one surface of the mounting element; and oneor more illuminating devices fixedly attached to the mounting element onthe surface containing the reflective element.
 5. The system of claim 4,wherein said mounting element comprises a printed circuit board.
 6. Thesystem of claim 4, wherein said one or more illuminating devicescomprise any one of the following: LED's and fluorescent lights.
 7. Thesystem of claim 1 wherein said electronic display is a liquid crystaldisplay.
 8. A method for controlling the amount of backlighting in anelectronic display device having a viewing surface and backlightassembly placed within a backlight cavity, the steps comprising: settinga maximum operating temperature for said backlight cavity; measuring thetemperature in the backlight cavity; dimming the backlight slightly whenthe temperature in the backlight cavity exceeds the maximum operatingtemperature; and measuring the amount of light contacting the viewingsurface; measuring the amount of light generated by the backlightingassembly; defining a preferred light ratio, wherein said light ratio isdefined as the ratio of the amount of light contacting the viewingsurface to the amount of light generated by the backlight assembly;calculate the current light ratio, based on said light measurements;increasing the power to the backlight assembly when the current lightratio exceeds the maximum preferred light ratio; and decreasing thepower to the backlight assembly when the current light ratio falls belowthe minimum preferred light ratio.
 9. A method for controlling theamount of backlighting in an electronic display device having a viewingsurface and backlight assembly placed within a backlight cavity, thesteps comprising: providing a power source which sends power to thebacklight assembly; providing a software driver which is operativelyconnected to and sends controlling signals to said power source; settingan operating temperature range for said backlight cavity; sending powerto said backlight assembly; measuring the temperature in the backlightcavity; slightly decreasing the power to the backlight assembly when thetemperature in the backlight cavity exceeds the operating temperaturerange; and holding the slightly decreased power amount until thetemperature in the backlight cavity returns to within the operatingtemperature range.
 10. The method of claim 9 further comprising thesteps of: measuring the power sent from the power source to thebacklight assembly; comparing the power measurement to the controllingsignals from the software driver; and modifying said controlling signalsif said power measurement does not match said controlling signals. 11.The method of claim 9 further comprising the steps of: measuring theamount of light contacting the viewing surface; measuring the amount oflight generated by the backlighting assembly; defining a preferred lightratio with a maximum and minimum tolerance, wherein said light ratio isdefined as the ratio of the amount of light contacting the viewingsurface to the amount of light generated by the backlight assembly;calculate the current light ratio, based on said light measurements;increasing the power to the backlight assembly when the current lightratio exceeds the maximum preferred light ratio; and decreasing thepower to the backlight assembly when the current light ratio falls belowthe minimum preferred light ratio.